1. Field of the Invention
The present invention relates to the field of energy conversion, particularly to conversion of thermal or electric microphenomena into macroscopic mechanical movements. The invention also relates to apparatus for carrying out the method.
2. Description of the Prior Art
Roughly, all physical phenomena can be divided into microscopic and macroscopic. In the context of the present invention, the term "microscopic phenomenon or movement" means the one which cannot be seen with the naked eye, whereas the term "macroscopic" relates to those phenomena and movements which can be seen with the naked eye. In the context of the present invention, macroscopic phenomena are those which are on the order of millimeters and kilograms, or greater values, whereas microscopic phenomena are those which are on the order of fractions of millimeters and grams, or smaller values, respectively.
Conventional prime movers, such as a.c. synchronous and asynchronous rotary electric motors, as well as d.c. motors used in various fields of industry operate on the principle of macrophenomena, such as rotation caused by interaction of electromagnetic fields of rotors and stators having windings. When the rotor and stator of such an electric motor are unrolled into planes, the motor is transformed into the so-called linear motor (Svecharnik, D. V. Linear Electric Drive [Lineiny Electroprivod], Energiya Publishers, Moscow, 1979). Other examples of application of macromovements are internal combustion engines, steam engines, etc.
However, the conventional prime movers operating on the principle of macrophenomena, i.e., rotary and linear electric motors, have the following common disadvantages: momentum of inertia during reversion of movement, considerable weight per unit power, difficulty in manufacturing, high cost of materials, inability of stopping in an accurate position caused by inevitable gaps and plays in the units of the electric motor and its reducer, if such is available, active and induction energy losses, etc. A disadvantage inherent specifically in linear motors is additional loss of energy associated with an open-loop nature of the magnetic circuit.
On the other hand, devices based on the use of microphenomena can be used only for microscopic movements, such as microscopic movements of phono stylus which are converted into electric signals in a record player, vibratory pumps, electromechanical actuators of control systems, etc. However, devices which operate on the principle of microphenomena, cannot be used as drive means or prime movers for macroscopic displacements.
Attempts have been made heretofore to solve above problems by converting micromovements into macromovements by means of special conversion devices.
An example of such a conversion device is a stacked piezoelectric ceramic displacement magnifying device described in U.S. Pat. No. 3,501,099 issued in 1970 to G. Benson. Benson shows two chambers, one which has a plurality of electroexpansive elements which may consist of piezoelectric material. The electroexpanisve elements increase their volume on reception of a high voltage signal. The chamber with electroexpansive elements contains an incompressible fluid. That chamber is sealed. In operation, the electroexpansive elements expand, which causes a volume change in the incompressible liquid and a volume change in the chamber which is at the broad surface of the piston. The volume change in the chamber in which the broad surface of the piston resides is greater than the volume change of the piezoelectric element, and therefore this change (the former of the two) functions as the multiplication means. The Benson device has means for protecting electroexpansive elements from an external load.
However, the Benson device is designed for carrying out only micromotions and, although theoretically it can work as a motion multiplicator, it is unsuitable for converting micromotions with such multiplicator rations which allow macromotions to be obtained.
This is because the initial volume of the electroexpansive elements of the Benson device which are contained in the incompressible liquid is extremely small, so that when such initial volume is multiplied, even by 100 times, the resulting multiplied volume still remains small. The reason is that by their nature the electroexpansive elements of the Benson device do not have a sufficiently developed surface perpendicular to the direction of expansion and therefore the volume of the chamber cannot be significantly increased.
Furthermore, the Benson device is based on the use of piezoceramic materials such as oxides of lead, titanium, and zirconium. It is known, however, that these materials lose their property of electroexpansion at pressures exceeding 15 kg/mm.sup.2. This means that, even at a volume multiplication factor of 100, the effective force should apply to such elements a pressure not exceeding 0.15 kg/mm.sup.2. Thus, the Benson the device cannot function as a power unit and cannot carry out work.
The electroexpansive elements of the Benson device comprise a stack of separate piezoceramic element utilizing an accumulated effect of expansion. In such a device, each element must be mechanically treated before assembly. This is because the piezoceramic element has a surface layer which absorbs a considerable portion of microdeformations, and this layer has to be removed. Furthermore, for strengthening the stack of elements must be bandaged.
The Benson has a protective device rather than an unloading device. This protective device shuts off the system when the load exceeds a predetermined load. This means that if the piezoceramic elements experience a high load, the device will be switched off rather than being unloaded and continuing to operate. The unloading system is needed in order to increase the power capacities of the device.